The retina is susceptible to injury in a variety of ways ranging from hereditary degenerative disorders to age related diseases. Due to the complexity of eye diseases and the difficulties of obtaining human retinal tissue for studies, human retinal disorders are very poorly understood, and much of the information concerning the subject is derived from investigation in animal models. Accordingly, this proposal will take advantage of our newly developed RPE cell transplantation paradigm involving the diseased eyes of rats. More specifically, we are able to transplant RPE cells into the subretinal space of neonatal and adult rat eyes. The grafted RPE cells, in turn, form a stable relationship with the host photoreceptor cells. Most significantly, we have been able to rescue degenerating photoreceptor cells by this RPE transplantation technique in two animal models, the Royal College of Surgeons rat, which exhibits an inherited retinal dystrophy similar to retinitis pigmentosa and the Fischer 344 rat, which demonstrates age related retinal cell death similar to peripheral and macular degenerations in man. The long-term objectives of this research are to: 1) better understand the mechanisms of retinal degenerative diseases as these relate to cell, tissue and humoral interactions through RPE cell grafting techniques; 2) develop possible therapeutic approaches and strategies in the treatment of similar human diseases; and 3) better understand what normal cellular, humoral and genetic interactions exist between RPE and photoreceptor cells that insure their survival and normal functional state. The specific aims of this research proposal involves a demonstration that one or more of the following mechanisms are involved in RPE transplant mediated photoreceptor cell rescue; 1) early post-transplantation restorative behavior of grafted RPE involving debris removal, cell division/spreading along Bruch's membrane and possible activation of host RPE in the RCS rat; 2) initiation by RPE transplants of a photoreceptor cell repair mechanism, involving outer segment regeneration in the RCS rat; 3) preservation by RPE transplants of the host retinal and choroidal blood vessels and blood/retina barrier integrity in RCS rats; 4) RPE transplant trophic factor involvement in photoreceptor cell rescue in RCS rats; and 5) RPE transplants and their trophic involvement in the delay of age related retinal cell death in the Fischer rat. The specific aims of this proposal will be accomplished through the use of light microscopy, electron microscopy, microsurgery, tissue transplantation, immunocytochemistry, tissue culture and molecular biology techniques.